The present invention relates to novel electrolytic cells and more particularly to such cells containing at least one electrode having platinum on a carbon support activated with a phosphorus-oxygen-containing compound. The present invention is also directed to a method of direct production of electrical energy using such cells.
In electrolytic cells, electro-catalyst electrode structures are employed to catalyze the electrochemical reaction necessary to produce electrical energy. For example, in a fuel cell, a fuel such as hydrogen, or a mixture of gases containing hydrogen in which hydrogen is the active constituent, is directly converted in a potentially low-cost process to electrical energy as a result of catalysts contained within the fuel cell. Such cells contain, for example, finely divided platinum at either the anodic or cathodic electrodes of the cell or at both electrodes of the cell.
One highly efficient type of cell employs platinum as the cathode electro-catalyst, phosphoric acid as electrolyte, and operates at elevated temperatures of up to, for example, 190.degree. C. However, a serious problem in using a supported platinum electro-catalyst in that environment, as well as other corrosive or acidic environments, is that the metal crystallites tend to coalesce with a consequence of significant reduction in its surface area over long term use. This has been known to reduce the catalytic activity to a great degree and significantly reduce useful fuel cell life. Such surface area loss is performance limiting in the cathode compartment where the electrocatalyst is employed. Of course, in those cells wherein the platinum is employed at only the anode or at both the cathode and anode, corresponding performance loss will occur. That is, in such cells, if it were not for this loss in catalytic activity, the fuel cell would have a much longer useful life.
The prior art is replete with teachings concerning various types of electro-catalyst systems for electrolytic cell electrodes and many catalytic materials have been suggested, including noble metals in addition to platinum, as well as various complexes of some of these. British Pat. No. 1,418,943 (Siemens Aktilngesellschaft), describes the use of various metal phosphide catalysts but nowhere teaches the use of platinum on phosphorus-oxygen-containing compound activated carbon supports. Various substitutes for platinum catalysts have been proposed. For example, in U.S. Pat. No. 3,449,169 (D. R. Rhodes), platinum phosphide has been suggested as an unsupported electro-catalyst primarily for use in the anode compartment. However, there is no suggestion that this compound could be supported or used in that state to prevent surface area losses. Unsupported platinum has far less surface area and thus, lower catalytic activity, than platinum on a high surface area support.